"Political prisoners will be released. But we still do not know whether all of them will be freed," a government official who wanted to be anonymous, said on Monday, adding that the pardon was expected "within days".

Another official said the release would come before President Thein Sein's official visit to India on Wednesday.

The release of the country's estimated 2,000 political detainees - who include pro-democracy campaigners, journalists and lawyers - has long been a top demand of Western nations which imposed sanctions on the impoverished country.

The tightly-controlled civilian government has reached out to critics including opposition leader Aung San Suu Kyi, freed in November last year after seven years of detention.

Her National League for Democracy (NLD) said it was "expecting" all political detainees to be released.

Nyan Win, the NLD spokesman, said he was optimistic that hundreds of the party's imprisoned members would be freed.

"We are expecting the release of all political prisoners," including student activists, he said.

'Dramatic developments'

Kurt Campbell, the US Assistant Secretary of State for East Asian and Pacific Affairs, hailed recent developments in Myanmar, including what he described as "very consequential dialogue" between Suu Kyi and the leadership.

Campbell, one of several US officials to held rare talks with Myanmar Foreign Minister Wunna Maung Lwin in Washington recently, said while concerns remain, "it is also undeniably the case that there are dramatic developments under way".

US President Barack Obama's administration has pursued both diplomatic engagement as well as continued sanctions against Myanmar.

"We have made clear our desire to see continued progress on issues such as prisoner releases," Campbell said at a Bangkok lecture.

He hinted that concrete moves towards democracy by Myanmar could lead to an easing of sanctions.

"We will match their steps with comparable steps," he added.

The new government, which came to power after controversial elections held a few days before Suu Kyi's release, appears keen to improve its international image and in August held the first talks between her and Thein Sein, a former general.

Suu Kyi, whose party won 1990 elections by a landslide but was never allowed to take power, has said she believes Thein Sein genuinely wants to push through reforms, but she cautioned it was too soon to say whether he would succeed.

The NLD boycotted last year's ballot, largely because of rules that would have forced it to expel imprisoned members.